The present invention relates to a method for fire extinguishing agent of certain dangerous combustible materials of which the fire can hardly be extinguished with conventional fire extinguishment agents when the material is once set on fire.
The hardly fire-extinguishable materials as the objective material of the present invention include those belonging to the following five groups of which (1) the first group includes powders of various metals such as magneisum, aluminum, zinc, titanium, zirconium, iron and the like, (2) the second group includes alkali metals such as sodium, potassium lithium and the like, (3) the third group includes water-prohibiting materials, i.e. materials which produce inflammable gases or evolve a large quantity of heat when contacted with water, such as calcium carbide, calcium phosphide, calcium oxide and the like, (4) the fourth group includes highly combustible inorganic solid materials such as red phosphorus, yellow phosphorus, sulfur, phosphorus sulfide and the like and (5) the fifth group include highly combustible liquid materials such as alkyl aluminums, alkyl lithiums, chlorosilanes, diketene and the like.
The materials of the first group, i.e. magnesium, aluminum, titanium and the like, are combustible and possibly explosive when they are in the form of a fine powder and may sometimes result in very serious hazards when a large amount thereof is set on fire. When the metal powder at a high temperature is brought into contact with water, a reaction may take place between the metal and water to produce hydrogen gas which causes explosion to scatter the metal powder so that water as a most conventional fire extinguishing agent can never be used when such a metal powder is set on fire. Other conventional fire extinguishing agents such as carbon dioxide gas, Halons and powder fire extinguishing agents are also ineffective for fire extinguishment thereof. The only known means having some effectiveness for fire extinguishment of fire on these metal powders is to sprinkle a powder of special chemicals such as sodium chloride, sodium carbonate and the like over the burning site of the powder so as to suppress the violence of the fire though only incompletely. The efficiency of this method is, however, quite low as a practical method because the sprinkled amount of the agent has to be so large to suppress the violence of fire and, even when the fire in the surface layer of the piled metal powder has been seemingly extiguished, the core portion of the pile still remains at such a high temperature of red heat as to result in re-ignition of the powder on exposure to fresh air so that disposal of the powder even after fire extinguishment must usually be postponed for a long time, for example, of 60 minutes or even longer.
The dangerous materials of the second group, i.e. alkali metals such as sodium and potassium, are notoriously reactive with water to produce hydrogen gas and a large quantity of heat to cause spontaneous ignition so that alkali metals must be strictly kept away from water. Other conventional fire extinguishing agents such as carbon dioxide gas, Halons and powder fire extinguishing agents are also ineffective for extinguishment of fire involving an alkali metal. The only method for extinguishment of fire involving an alkali metal is to sprinkle dry sand over the burning site of the alkali metal although sprinkling of a powder of special chemicals such as sodium chloride, sodium carbonate and the like may have effectiveness in some cases. As a natural consequence of the principle of fire extinguishment with these conventional agents relying on the suffocating and cooling effects, a quite long time is taken for complete extinguishment of fire involving an alkali metal in addition to the disadvantage that a large amount of the fire extinguishing agent is required for complete extinguishment.
S. J. Rodgers, et al. have reported in MSA Res. Corp. First Quart. Progress Rept., Contract AF-33 (657)-8310, June 15, 1962 on the results of their experiments for extinguishment of fire involving each 1 g of an alkali metal such as lithium, sodium and potassium by sprinkling either one of 41 kinds of inorganic powdery materials. Their investigations have resulted in the proposal of powders of four kinds of materials including sodium carbonate, sodium chloride, potassium chloride and graphite as a practically effective fire extinguishing agent on an alkali metal. Although the above mentioned 41 kinds of powdery inorganic materials included boron oxide B.sub.2 O.sub.3, no promising results could be obtained with boron oxide, presumably, because they undertook any controlling means for the purity of and moisture content in the boron oxide used as a fire extinguishing agent.
Namely, a conventional product of boron oxide usually contains at least a few % of water, which may be in the form of boric acid H.sub.3 BO.sub.3. When such a water-containing boron oxide is sprinkled over a burning site of fire on an alkali metal, a loud noise of boiling is caused. This is presumably because, when the boron oxide is contacted with the alkali metal at a high temperature, the water contained in the boron oxide is decomposed and vaporized into water vapor a portion of which which in turn reacts with the alkali metal to produce explosive hydrogen gas. The inventor has noted in his experiments that, in the course of melting and vitrification of boron oxide sprinkled over fire, the water vapor produced forms a numberless large bubbles which subsequently coalesxe into larger ones in the molten boron oxide so that complete coverage of the burning site of the fire can never be obtained not to give an effect of fire extinguishment by suffocation as high as desired.
The dangerous material of the third group is a water-prohibiting solid material such as calcium carbide and calcium oxide. When these water-prohibiting materials are contacted with water, a large quantity of heat is evolved and or inflammable gases, such as acetylene, are produced to cause fire. These materials are sometimes reactive with most of conventional fire extinguishing agents. Therefore, these materials belong to the class of hardly fire-extinguishable materials in the absence of any effective method for fire extinguishment. The only means to have some effectiveness for fire extinguishment is sprinkling of dry sand over the burning site although the practical value of this method is relatively low due to the so large amount of the dry sand required for fire extinguishment in addition to the sometimes unavoidable incompleteness of extinguishment.
The dangerous material of the fourth group is a combustible solid materials such as red phosphorus, yellow phosphorus, sulfur and the like. These materials are readily ignited at a relatively low temperatures and burn at a high velocity. Some of them are toxic in themselves or may produce toxic gases in burning to cause troubles and difficulties in the fire extinguishment works thereof.
The dangerous material of the fifth group is a readily combustible liquid. Furthermore, some of them such as, for example, alkyl aluminums and chlorosilane compounds react violently with water so that water can never be used for extinguishment of fire involving these combustible liquids. Other conventional fire extinguishing agents such as carbon dioxide gas, Halons and powder fire extinguishing agents are absolutely or relatively ineffective for extinguishment of fire involving these combustible liquids.